Device for preventing back-flow in centrifugal pumps operating in parallel

ABSTRACT

A device for preventing back-flow through one of several centrifugal pumps connected in parallel in a common circuit when the impeller of the pump is stationary. The device has a closure member in the form of a cylindrical relatively rotationally displaceable closure element, which in one position permits free passage of the back-flow and in another position closes off the back-flow. The closure element has guide elements which are angularly displaced about the axis of rotation of the pump impeller in one direction by the swirl of the stream of medium being conveyed.

United States Patent [191 Laing I 1 Dec. 17, 1974 1 1, DEVICE FOR PREVENTING BACK-FLOW IN CENTRIFUGAL PUMPS OPERATING IN PARALLEL [76] Inventor: Nikolaus Laing, l-lofener Weg 35-37, 7141 Aldingen near Stuttgart, Germany 22 Filed: Sept. 28, 1972 21 Appl. No.2 293,141

[30] Foreign Application Priority Data Oct. 7, 1971 Austria 8658/71 [52] US. Cl 417/424, 417/286, 417/300, 415/146, 415/158, 137/455, 137/511 [51] Int. Cl. F04b 17/00 [58] Field of Search 417/424, 426, 286, 300; 415/146, 147,158, 159; 137/455, 511, 499

[56] g References Cited UNITED STATES PATENTS 1,065,208 6/1913 Brauer 415/159 1,482,547 Dell 137/49, 1,725,344 8/1929 Dennis....., 415/158 2,186,988 l/l940 Osborne 415/159 2,336,010 12/1943 Gregory et a1... 415/159 3,276,384 10/1966 Boone et al v. 415/146 3,589,829 6/1971 Schetinin v 415/159 Primary ExaminerC. J. Husar Attorney, Agent, or FirmPennie & Edmonds 57 ABSTRACT A device for preventing back-flow through one of sev-- eral centrifugal pumps connected in parallel in a common circuit when the impeller of the pump is stationary. The device has a closure member in the form of a cylindrical relatively rotationally displaceable closure element, which in one position permits free passage of the back-flow and in another position closes off the back-flow. The closure element has guide elements which are angularly displaced about the axis of rotation of the pump impeller in one direction by the swirl of the stream of medium being conveyed.

4 Claims, 3 Drawing Figures PATENTED m 1 71974 $854,848

SHEET 2 95 3 Fig.2

DEVICE FOR PREVENTING BACK-FLOW IN CENTRIFUGAL PUMPS OPERATING IN PARALLEL THE PRIOR ART In the operation of a plurality of centrifugal pumps connected in parallel in a circuit, a characteristic is defined in which'the magnitudes of the pressures coincide with the maximum pressure of the individual pumps, whilst the quantity is given by the sum of the individual quantities. The operating point is given by this summation characteristic and its intersection with the throttling characteristic of the system, against which the pumps, connected for multiple flow, operate:

If now one of the pumps shuts down, the liquid being conveyed flows back through this pump, counter to the desired direction of through-flow, into the inlet region.

Thereby the pumping action of the pump unit 001- rupting the back-flow in such pumps have been found unsuitable, since for the purpose of openingthese valves a continuous pressure differential has to be maintained which results in considerable overdimensioning of the pump and appreciable increase in the power consumption of the driving motor. Moreover, particularly in the case of axial flow pumps, great difficulties are encountered in starting up against closed valves, since axial flow pumps are unstable in the region of low throttling values, so that in certain circumstances the minimum pressure required for opening the valves is not reached at all.

THE OBJECT OF THE INVENTION The object of the invention is to provide for a closure device which automatically interrupts the through-flow through a pump, when the pump impeller is not in operation and which does not require any significant.

openingand closing pressure.

DESCRIPTION OF THE INVENTION The back-flow preventing means according to the invention is constructed on the principle of a cock. In accordance with the invention it is operated not by the pressure of the turbine machine, but by the swirl in the FIG. 2 shows diagrammatically asection through the lower portion of the boiling water reactor shown in FIG. 1, in which however only the most essential elements are shown.

FIG. 3 shows partly in elevation and partly section a pump with a slide mechanism in accordance with the invention, which automatically-prevents any throughflow in the pump when the pump impeller is not in operation. l

- The boiling water reactor shown in FIG. 1 has a pressure vessel D, which encloses the core K and the envelope chamber M. In the'envelope chamber M pumps P embodying the invention'are located in which the motor, the stator and the pump impeller each form a unit, which is suspended by the supply leads Z in the envelope chamber.

FIG. 2 shows, again diagrammatically, the lower por tion of the reactor shown in FIG. l.. The control rods 2 are surrounded by an envelope 3. The pumps P are located in the envelope chamber M.'-The through-flow takes place in the direction of the arrows 6 and 6, i.e. downwardly in the envelope chamber M and upwardly in the core chamber of the reactor. The pumps P-are joined to the upper portion of the pressure vessel D by their electrical power supply leads 7 and inserted in a ring 8 which has an aperture for each pump.

In the embodiment shown in FIG. 3, the stator of the pump motor consists of the pole teeth which are formed by radial sheet metal elements. The magnetic return path is provided by annularsheet metal packets 51 and 51. The coils of the winding 52-each have one turn only and they'are connected to supply leads 53 which again form a conductor; bundle by which the pump is suspended. Through apertures 54 and 55 the medium being conveyed can flow intothe stator chamber and .cool the stator. The frontal surfaces 56 of the pole teeth form a magnetic gap 57. The rotor consists of iron core 58, the bars 59 and short-circuiting rings 60 and 61 of a cage winding. The surface of the rotor facing the air gap 57 lies in a spherical annular region. The rotor is, as in the case of the embodiment'according to FIG. 3, supported by a sphere 62, a dish 63 seflow which is present in the case of every centrifugal machine. Moreover there is even the possibility of converting into pressure the energy content of the swirl which would otherwise be lost. It has been found that devices in accordance with the invention open in every case and that they not only have such a low resistance that practically no pressure loss is produced, but moreover introduce the possibility of producing a gain in pressure by conversion of the after-swirl into pressure.

FIG. I shows in diagrammatic and partially sectioned elevation a boiling water reactor in which pumps embodying the invention are located.

cured to the stator as well as a dish 64 secured to the rotor. This dish 64 is arranged on a column 65 whichis joined to the rotor viascrew connections. A ring 63' serves the purpose of preventing the rotor from falling down when the pump is shut down. The guide blade ring 66 is secured to the stator, whilst the pump blade ring 67 is located on the rotor. The medium flowing round the stator is conveyed in the direction of the arrow 69 by the pump into a fluid discharge area of the pump where it enters a fixed valve member or end housing 70 of a cock or valve, after which it is discharged through slots 71. In the fixed valve member, a rotatable valve member 73 having a slightly conical inner surface 74 as well as a cylindrical outer surface 75, is supported in the bearings 72 and 72. The outer surface of the rotatable valve member has axially extending slots, which are adapted to register with the slots 71 of the valve member 70. The regions 75' between the slots 71 extend in an azimuth direction over a somewhat greater distance than that over which the slots 71 extend in an azimuth direction, i.e. the regions between these slots 71 are somewhat-wider than the latter. In the same way the bridges or space 77 between the slots in the outer cylinder 75 of the rotatable membet valve are somewhat wider than the slots 71 of the fixed valve member.

Secured to the member 73 is a guide blade ring 78 whose blades are so directed that the member is rotated by the swirl of the hydraulic medium in one direction up to an abutment. In this position the slots of the valve register with the slots of the end housing and the bridges of the rotatable member with the bridges of the fixed member. This means that when the pump is operating the medium can freely flow in the direction of the arrow 69 through the pump chamber and be discharged therefrom in the direction of the arrow 80. If now the flow is interrupted for any reason, a spirally wound spring 81 which biasses the rotatable member in the opposite direction to that in which it is turned by the swirl of the flow of medium, causes an angular displacement of this valve member in the opposite direction up to a second abutment. In this position the slots in the outer cylindrical wall 77 of the rotatable member come into register with the bridges 75 of the fixed member on the one hand, and the bridges between the slots in the outer cylindrical wall of the rotatable member with the slots 71 of the fixed member on the other hand. ln this position the valve defined by the fixed valve member and the moveable valve member 73 is closed, so that if for example the pump shuts down, no flow of medium produced by adjacent pumps can flew back through it. Thereby the possibilty of a. shunt path for the medium through shut-down pumps is eliminated.

lt is pointed out that the support of the cock 73 can be adjusted by means of a screw 82 which presses on the bearing dish 83. Relief bores 84 provide pressure equalization. Outwa'rdly conical feet 85 facilitate insertion of the pump into the sheet metal ring 86 during installation. Other devices for adjusting the bearing may be provided in place of the screw 82.

I claim:

l. A flow. responsive valve device for preventing back-flow of fluidthrough a centrifugal pump when the pump is not operating and when said pump creates a fluid swirl in a pump discharge area when the pump is operating, said valve device comprisinga fixed valve member in the discharge area having apertures therein, a rotatable valve member in the discharge area having apertures therein adapted in a first rotatable position thereof to overlie the apertures in said fixed member to allow fluid flow through the apertures and in a second rotatable position thereof tobe masked by the space between the apertures of said fixed member to' prevent fluid flow through the apertures, spring means urging said rotatable valve member towards said second rotat able position, andblading on said rotatable member cated in said discharge area adapted to be contacted by the fluid swirl when said pump is operating to urge said rotatable member to the first position against the force of the spring means such that the apertures of the first and second members overlie each other when the pump is operating.

2. A flow responsive valve device according to claim 1 wherein eachsaid valve member comprises a hollow cylinder and wherein said apertures comprise slots with 

1. A flow responsive valve device for preventing back-flow of fluid through a centrifugal pump when the pump is not operating and when said pump creates a fluid swirl in a pump discharge area when the pump is operating, said valve device comprising a fixed valve member in the discharge area having apertures therein, a rotatable valve member in the discharge area having apertures therein adapted in a first rotatable position thereof to overlie the apertures in said fixed member to allow fluid flow through the apertures and in a second rotatable position thereof to be masked by the space between the apertures of said fixed member to prevent fluid flow through the apertures, spring means urging said rotatable valve member towards said second rotatable position, and blading on said rotatable member located in said discharge area adapted to be contacted by the fluid swirl when said pump is operating to urge said rotatable member to the first position against the force of the spring means such that the apertures of the first and second members overlie each other when the pump is operating.
 2. A flow responsive valve device according to claim 1 wherein each said valve member comprises a hollow cylinder and wherein said apertures comprise slots with the space between adjacent slots being at least as wide as the slots.
 3. A flow responsive valve device according to claim 1 having in addition two spherical bearings mounting the rotatable valve member where the center of both bearings lie on the longitudinal axis of the pump, and adjustable means for moving one of said bearings in an axial direction.
 4. A flow responsive valve device according to claim 3 wherein said spring means comprises a spiral spring. 